duplicated objects dont show up in render
I can resolve it for you - but I don't really know why?

If you run your animation (before deleting the keyframes) all three objects are instantly moved on top of each other. So it is probably rendering all duplicates, it is just that they are on top of each other. I wonder if it has something to do with Blender effectively starting the frame 1 animation prior to rendering an image? Someone smarter may be able to help here.

Anyhow, for the duplicated objects remove the associated keyframes (in the Animation workspace) and now the duplicates are now rendered.

Here is a rendered output example.